The Battle of Drøbak Sound took place on April 9, 1940, during the early stages of World War II, when the German naval force attempted to seize the Norwegian capital of Oslo.

Opposing the invaders, an outdated fortress located in the Fjord, manned by trainees and older reservist soldiers.

Despite being out manned and out gunned, the defenders delivered a mighty blow to the German forces, sinking the cruiser Blücher and prolonging the invasion.

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The Prelude To The Battle

Europe was in the throes of World War II and the entire continent was a high-stakes chessboard, with countries constantly shifting their allegiances and strategies, and Norway was no exception.

Germany’s rapid expansion across Europe had far-reaching effects, and Norway, strategically situated in Northern Europe with coastlines facing both the Atlantic Ocean and the Arctic Sea, gained significant attention.

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Norway’s geographical position made it a prime and tempting target for Hitler’s Third Reich for several reasons. Its long rugged coastline, dotted with numerous fjords, offered an excellent naval base for German submarines to disrupt Allied shipping in the North Atlantic.

Equally important, Norway was a gateway to Sweden’s northern iron ore fields in Kiruna, which the Germans heavily relied on for their war machine.

Besides, the security of supply lines was of utmost importance to Germany. The German-occupied, ice-free ports on the Norwegian coast, like Narvik, offered a convenient and safe way to import iron ore from Sweden without the risk of British naval blockades.

In April 1940, Operation Weserübung, the German plan for the Invasion of Denmark and Norway, was put into action. The initial phase saw rapid German advances and quick surrender of Denmark. But Norway, determined to maintain its neutrality and independence, resisted.

On the 9th of April, the German navy attempted a strategic coup by launching simultaneous attacks on several Norwegian ports, including Oslo, Narvik, Bergen, Stavanger, and others.

The goal was to swiftly secure the ports, take control of the strategic points in the country, and install a pro-German government led by pro-Nazi politician Vidkun Quisling.

In the early hours of that day, the German heavy cruiser Blücher, packed with nearly a thousand troops and Gestapo officers, sailed into the Drøbak Sound, attempting to seize Oslo.

They underestimated the Norwegian defenses at Drøbak Sound, within the Oslofjord.

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The location was defended by Oscarsborg Fortress, a centuries-old naval-defense bastion, albeit considered obsolete by many. A tripwire was set, where the German naval force would be met with resistance unbeknownst to them.

The Germans wrongly assumed that the fortress was unarmed and would easily surrender.

The Defenders Of Drøbak Sound

During the early hours on April 9, 1940, the German naval forces came face-to-face with the defensive might of the Norwegian forces at Oscarsborg Fortress.

Positioned strategically within the Drøbak Sound at the Oslofjord’s narrowest point, the fortress posed a significant roadblock to navigation – its prime role being to protect the Norwegian capital, Oslo.

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The stalwarts at the fortress, led by Colonel Eriksen, consisted of an army of roughly 500 soldiers. With a majority as recruits armed with only a few weeks of training.

Colonel Eriksen, commander of the Oscarsborg.

The fortress’s primary line of defense were the three monumental, albeit antiquated, cannons fondly named “Moses,” “Aaron,” and “Joshua.” These, along with other smaller cannons, torpedoes, and underwater mines composed the “Kalvøya” layer, the fortress’s southeastern defensive strata.

The Attackers

The German naval force was led by the cruiser “Blücher,” the flagship of the German flotilla, supplemented by the heavy cruiser “Lützow,” and several smaller warships.

The flotilla transported around 2,000 soldiers intended to capture Oslo and quickly subdue the Norwegian government. The Germans were operating under Operation Weserübung, intending a surprise attack on numerous Norwegian coastal cities simultaneously, an unprecedented move in military history.

One of the three Krupp 280 mm guns at the fortress.

Favoring speed over defense, the Germans didn’t dispatch reconnaissance units prior to the flotilla’s voyage into the fjord, which proved to be a critical mistake.

The Battle Of Drøbak Sound

The German strategy was swift and decisive action, intending to seize the whole of Norway before any significant resistance could materialize. Achieving surprise was crucial in their plan.

For the Norwegians, the strategy was to delay the Germans as much as possible to buy time for mobilization and evacuation of the Royal family and the Government.

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In the early morning of April 9, the German flotilla entered into the Drobak Sound where Oscarsborg Fortress lay. Although taken by surprise, and with their primary guns dating back to the 19th century not equipped with either telescopes or range tables for the necessary distance, Colonel Eriksen made the decision to open fire.

On echoing Eriksen’s order to fire, “Either I will be decorated, or I will be court martialed. Fire!”, around 04:30, the fortress came alive.

A direct hit on the Blücher’s control tower critically damaged the ship and created havoc, massively disrupting the German plan. A second hit from one of the fortresses 280 mm Krupp guns started a fire midship on the Blücher.

Followed up by a torpedo attack, the Blücher was fatally wounded and was evacuated by the crew. It capsized and sank, taking with it over 1,000 men.

Blücher on fire and sinking in the Drøbak Sound.

The attack by the fortress was devastatingly effective, with Blücher being sunk by cannon fire and torpedoes, causing significant delay to the German invasion plans. It resulted in the successful evacuation of the Norwegian Royal family, national gold reserves, and legislators.

How dееp is Drobak sound?

Drobak Sound is approximately a milе widе and has a maximum dеpth of about 200 mеtеrs. It’s stratеgically locatеd within thе Oslofjord, dividing it into two branchеs. The branches are hindеrеd by obstaclеs likе an artificial subsurfacе jеtty and a shoal. Dеspitе its narrownеss, it plays a crucial role in controlling thе watеr еxchangе bеtwееn thе outеr and innеr Oslofjord. Thus affecting its hydrography and influеncing pollution lеvеls.

The Aftermath

However, the loss of the Blücher and the fatalities incurred by the Germans at Drøbak Sound were not enough to deter Nazi Germany’s occupation of Norway.

The German cruiser Blücher, listing before sinking.

The invading forces regrouped and the city of Oslo was seized later that day. On the morning of April 10, Eriksen surrendered the fortress to the German invaders.

By June 1940, just two months after the battle, all strategic Norwegian ports were under German control.

This occupation set the stage for a prolonged, resource-intensive military defense against Allied efforts to liberate Norway, diverting crucial time, attention, and military resources that could have been used elsewhere in the war.

The implications of the Battle of Drøbak Sound extended beyond Norway. The successful invasion and occupation of Norway, in spite of the setback at Drøbak Sound, allowed Germany to secure its supply of critical war resources, particularly iron ore from Sweden, which was shipped out of Norway.

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The German presence in Norway also gave the Nazis control over the North Atlantic and a strategic advantage against the United Kingdom.

Simultaneously, the Battle of Drøbak Sound marked a significant moment in World War II for its psychological effect. For nations yet untouched by the war, it was a sobering display of Germany’s military prowess and intent. The battle, along with the ensuing occupation, highlighted that neutrality was no guarantee.